Temir arch is in the eastern part of the North Caspian depression on the northern margin of the Aktyubinsk-Astrakhan zone of basement highs. The Temir zone of highs is recognized on reflecting horizon P-2, which is at the top of the Visean-Bashkirian carbonate complex. This upper Visean-Bashkirian carbonate platform is about 500 m thick and rests on Upper Devonian-Carboniferous clastics. It is bounded by zones of abrupt subsidence of horizon P-2, imparting to it the form of a narrow structural nose that extends 150 km north from Kenkiyak.
Overlying the upper Visean-Bashkirian carbonates are Upper Carboniferous-Lower Permian clastics, at the top of which is reflecting horizon P-1. These clastics resulted from the Hercynian orogeny in the Urals, which are directly to the east. Temir arch is not expressed on horizon P-1.
Seismic survey data are the basis for recognizing three quasi- synchronous seismic complexes in the sedimentary pile beneath the Lower Permian Kungurian salt. These are bounded by discordances, which coincide with reflecting horizons P-1, P-2, P'-2, and P-3.
The upper seismic complex is between reflecting horizons P-1 and P-2 and consists of Upper Carboniferous-Lower Permian clastics. In Ostansuk well P-38 the Upper Carboni- ferous is largely dark gray argillite along with beds of sandstone. Thickness is 1.1 km. Elsewhere this part of the section is argillite, sandstone, and conglomerate and is only 0.2 km thick. The Lower Permian is predominantly dark argillite and is hundreds of meters thick. Total thickness of this seismic complex ranges fro 0.4 to 2 km.
The seismic complex between reflecting horizons P-2 and P'-2 is upper Visean-lower Moscovian limestone. These two reflectors merge toward the west, indicating erosion of this complex before deposition of the overlying complex.
The complex bounded by reflecting horizons P'-2 and P-3 is the Upper Devonian-Tournaisian section. As of 1986 it had not been reached by the drill; however, the seismic data suggest that it is a thick carbonate atoll. Its structure has not been studied in any detail, but on P'-2 it has an amplitude of about 1.5 km and dimensions of 120 by 40 km. Maximum thickness of this builup is 2 km.
Temir arch may extend farther south to the Tobusken structure and also to the northwest another 30-50 km. Morphologically this arch is almost identical to Astrakhan arch and Karaton high, the atoll nature of which has been established. These three large structures have identical structural positions. The hydrocarbon potential of Temir arch has been assessed as substantial.
Taken from Akishev and others, 1986; digested in
Petroleum Geology, vol. 23, no. 7/8, two structure maps
and two cross sections.
Copyright 2003 James Clarke. You are encouraged to print
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